The present invention relates to a spindle control device, and particularly to a spindle control device in an optical disk recording/reproducing apparatus in which one frame of a composite video signal (including synchronizing signals such as a horizontal synchronizing signal, a vertical synchronizing signal, and the like) is recorded on each track on an optical disk (including an opto-magnetic disk and a phase-change type optical disk) having a vertical synchronizing mark, and the recorded signal on the optical disk is reproduced or erased.
In a conventional reproducing-only video disk player, since an optical disk to be played carries a composite video signal already recorded thereon, the composite video signal is read from the optical disk and demodulated. A phase difference of a reproducing horizontal synchronizing signal, included in the demodulated composite video signal relative to a reference horizontal synchronizing signal, is detected so as to perform spindle servo control in accordance with the detected phase difference.
On the other hand, in a system in which one frame of composite video signal is recorded on each track on an optical disk and the recorded signal is reproduced or erased, no composite video signal exists on the disk before recording. Therefore, it is not possible to perform spindle servo control using a reproducing horizontal synchronizing signal, unlike the above-mentioned reproducing player. Accordingly, a vertical synchronizing mark VM, made of a mirror portion where no pregroove G is cut, is provided for every rotation on a disk, for example, at its inner circumference (or at its outer circumference) as shown in FIG. 1. The vertical synchronizing mark VM is detected by a vertical synchronizing mark detector, such as a photocoupler or the like, during a recording operation, and spindle servo control is performed, so as to make the detection timing of the vertical synchronizing mark VM agree with a predetermined position on the time base of the composite video signal to be recorded. As a result, the irradiated position, with a recording light beam modulated in accordance with the composite video signal, is controlled to be a predetermined position in the circumferential direction of the disk at the detection timing of the vertical synchronizing-mark detector.
Such a system is arranged so that, in the case where the detection timing of the vertical synchronizing mark is displaced relative to the composite video signal to be recorded as shown by a broken line in FIG. 2, the position of the vertical synchronizing mark detector is moved to adjust the relative position mechanically on the time base between the composite video signal to be recorded and the detection timing of the vertical synchronizing mark to be as shown by a solid line in FIG. 2. Accordingly, it is difficult to perform the adjustment, because the adjustment of the relative position is performed by mechanical adjustment of the position of the vertical synchronizing mark detector. There is a further defect in that the displacement is caused easily because the vertical synchronizing mark detector cannot be fixed firmly.